Only applies if you have cache device such as a ssd, when ZFS was created, ssd’s where new and could only be written to a few times, so zfs has some prehistoric limits to save the SSD of the hard labor. l2arc_write_max is such a value, by default only 8mb/s can be written to the ssd. Clearly you can increase this. (at the cost of more SSD use)

HD Tune Pro is a hard disk / SSD utility with many functions. It can be used to measure the drive's performance, scan for errors, check the health status (S.M.A.R.T.), securely erase all data and much more.

In fact it's only recently that we've finally seen some progress on this front. JMicron's introduction of a PCIe 3.0 x2 to USB 3.1 Gen 2 bridge chip (JMS583) has enabled Asian OEMs to introduce bus-powered NVMe SSD enclosures with a USB interface, finally enabling relatively cheap USB adapters for NVMe drives. MyDigitalSSD, in turn, is one of the first to bring such a device to the North American market with their M2X External USB 3.1 Gen 2 M.2 NVMe PCIe SSD Enclosure Adapter.

“SSDs store their data electrically, in a fashion that isn’t amendable to cusomary data recovery tools. Once an SSD fails, it’s literally a black box. On the other hand, there are some instances in which the failure of a hard disk makes it possible for data recovery services to extract a subset of the data in the drive. It’s expensive, but it can be done.”